A male fly walks into a bar and orders cornmeal-molasses- yeast. A pretty female fly comes and sits next to him. They look at each other, he starts to say hello, but then she orders some starch. He turns away. She looks at his glass of cornmeal- molasses -yeast and gets up to leave.

A recent study, published in the Proceedings of the National Academy of Sciences, shows that mating preference of fruit flies (the ones you see swarming near a piece of rotten fruit) is dependent on their diet because it changes the composition of bacteria that live in their gut (gut microbiota). This intriguing study stems from previous experiments in which fruit flies bred under different environmental conditions preferentially mated with other fruit flies from the environment in which they have been reared.

Gil Sharon and his colleagues at Tel Aviv University in Israel and University of Maine in the United States decided to experiment with food sources and see if they induce preferential mating in fruit flies. They reared one population of fruit flies on a diet of cornmeal, molasses and yeast for 37 generations and another population on starch for the same amount of time. After eleven generations, the flies showed preferential mating when the populations were mixed in equal proportions. Of the 38 recorded matings observed 29 were homogamic (i.e. “starch males” and “starch females” or “CMY males” and “CMY females”).

However, this trend was abolished if the fruit flies were fed antibiotics before the two populations were mixed. Of the 38 recorded matings in this experiment only 18 were homogamic whilst the other 20 were heterogamic. Antibiotics are chemicals that target bacteria, and this experiment suggests that the bacteria living in the gut of the fruit fly might have some role to play in who they chose as a mate.

After fingerprinting the gut microbiota, the authors noticed that eating starch led to enrichment of a particular type of bacteria in the “starch flies”. This increase in number corresponded to a change in cutaneous hydrocarbons (CH) secreted by the “starch flies”. CH are components of sex pheromones (sex pheromones are chemicals that animals secrete to convey their species and type and attract similar mates) in fruit flies and play an important role in mate selection. Hence, an altered composition of CH would mean that the “starch flies” would smell very different compared to the “CMY flies”. How the “starch flies” respond to their own altered sex pheromones is a question that is yet unaddressed….

The role of commensal gut bacteria in influencing behavioral patterns is an intriguing aspect of evolution. Think about it when you walk into a bar….

Comments

So would this be considered a legitimate example of inducing reproductive isolation in a lab experiment–an artificial example of how different environments could lead to separate population being unable to mate in the future?

Very interesting. I’d be curious to know more about the different gut microbes. Since we know that bacteria reproduce sexually, so I wonder if it is possible that they have somehow hijacked the fruit flies in order to ensure reproductive success. We know parasites can hijack organism’s behavior, why not bacteria?